This invention relates to a high density mobile storage system, and more particularly to an actuator mechanism for a mechanical assist mobile storage system.
A mechanical assist mobile storage system typically includes a series of storage units movable on a transversely extending rail arrangement. Each storage unit includes a chain-driven assist mechanism which moves the storage unit on the rail arrangement in response to manual operation of a rotatable actuating handle. Rotation of the handle results in rotation of a drive sprocket. A chain is trained about the drive sprocket as well as the remaining components of the drive system, such that rotation of the handle and drive sprocket provides movement of the chain to operate the components of the drive system. The chain is engaged with a sprocket mounted to an adjustable tensioning arm, which is operable to maintain an appropriate amount of tension in the chain.
In an existing assembly, the handle is mounted to a rotatable hub which is mounted to the outer end of a shaft. The drive sprocket is mounted to the inner end of the shaft, such that rotation of the handle imparts rotation to the drive sprocket through the hub and the shaft. While this arrangement operates satisfactorily, problems can arise when an excessive amount of torque is applied to the handle, such as when the storage unit has reached the full limit of its travel and force is still applied to the handle, or when an operator attempts to crank the handle with a force beyond that required to attain maximum speed of movement of the storage unit. In such situations, the excess force applied to the handle can result in excessive wear or stretching of the chain, or can cause movement of the chain tensioning mechanism out of position. In either case, a service call is typically required to return the unit to an operative condition, typically by adjustment of the chain tensioning mechanism.
It is an object of the present invention to provide a mechanical assist mobile storage system which eliminates the adverse effects experienced by the components of the drive system upon application of excessive force to the handle beyond that required to move the storage unit at its maximum speed. It is a further object of the invention to provide an actuator arrangement which isolates the handle from the components of the drive system when an excessive force is applied to the handle. A still further object of the invention is to provide such an actuator arrangement which is simple in its design and construction, yet which functions effectively to prevent the drive sprocket from experiencing excessive forces. A still further object of the invention is to provide such an actuator arrangement which is inexpensive to incorporate into the drive system and which substantially reduces or eliminates the need for service calls resulting from application of excessive forces to the actuator handle of a mechanical assist mobile storage system.
In accordance with the invention, an actuating arrangement for a mobile storage system includes an actuator handle rotatably mounted to a storage unit and a drive arrangement located within the storage unit for moving the storage unit in response to operation of the actuator handle. A torque limiting mechanism is interposed between the handle and the drive arrangement. The torque limiting mechanism is operable to transmit torque to an input or drive shaft of the drive arrangement upon manual rotation of the handle by an operator, to provide movement of the storage unit. The torque limiting mechanism is further operable to prevent transmission of torque to the input shaft exceeding a predetermined threshold, so as to isolate the input shaft from excessive torque resulting from application of a force to the actuator handle beyond that required to move the storage unit at its maximum speed of movement.
The torque limiting mechanism includes a hub member operatively connected to the actuator handle. An input member is mounted to the input shaft such that an end portion of the input shaft extends from the input member. The hub member includes a passage within which the end portion of the input shaft is received. A retainer member is secured to the end of the input shaft and engaged with the hub member, so as to retain the hub member in position on the end portion of the input shaft. The hub member and the input member define facing surfaces, which are preferably spaced slightly apart from each other.
A torque limiting coupling arrangement is interposed between the facing surfaces of the hub member and the input member, and is operable to isolate the input shaft from excessive forces applied to the actuator handle. In one version, the torque limiting coupling arrangement is in the form of a series of spherical engagement members, each of which is received within a passage which is preferably formed in the hub member. The hub member passages open onto the surface of the hub member which faces the input member, and the engagement members protrude from the surface of the hub member. Engagement structure is formed in the facing surface of the input member, and the engagement members are selectively received within the engagement structure of the input member for coupling the hub member to the input member, and thereby the actuator handle to the input shaft.
A spring is received within each passage of the hub member, and urges each engagement member outwardly from the surface of the hub member toward the input member, so as to bias the engagement members toward an engaged position in which the engagement members couple the hub member and the input member together. Each spring is retained in position by means of an adjustment member, which enables an operator to adjust the biasing force exerted by the spring on its respective engagement member. Upon application of a force exceeding the predetermined threshold, each engagement member is movable away from its engaged position against the force of its respective spring, go as to de-couple the hub member from the input member. When this occurs, the hub member spins on the end portion of the input shaft without transfer of force from the input handle to the input shaft, and the engagement members ride on the surface of the input member. When the force applied to the actuator handle falls below the predetermined threshold, each engagement member returns to its engaged position in which the engagement member is seated within the engagement structure formed in the surface of the input member, to couple the hub member to the input member and to thereby enable rotation of the input shaft in response to rotation of the handle.
In another version, the torque limiting coupling arrangement is in the form of a slip disc engaged between the facing surfaces of the hub member and the input member. The hub member and the input member are pressed tightly together and are engaged in a friction engagement fit through of the slip disc. Upon application of a force exceeding the predetermined threshold, the frictional engagement provided by the slip disc is overcome and the hub member spins on the end portion of the input shaft without transfer of force from the input handle to the input shaft, so as to de-couple the hub member from the input member. When the force applied to the actuator handle falls below the predetermined threshold, the slip disc is once again operable to couple the hub member to the input member through friction and thereby enables rotation of the input shaft in response to rotation of the handle. In a preferred form, an adjustable pressure member, such as a Belleville spring, is interconnected between the hub member and the input member for varying the frictional engagement provided by the slip disc and thereby the threshold force which de-couples the hub member and the input member.
The invention also contemplates a method of actuating a drive arrangement associated with a mobile storage unit, substantially in accordance with the foregoing summary.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.